0320032

We propose for 260 ks of INTEGRAL time to perform a ToO observation of a transient millisecond X-ray pulsar in outburst. The target can be either one of the five known transient accreting millisecond X-ray pulsars in the case of a new outburst or a newly observed object of this class. The program will be performed in coordination with a 150 ks observation on the XMM-Newton satellite in order to study in detail the broad band spectrum and timing properties of the source during its outburst. Since these sources are a new class of astronomical objects this coordinated study will be essential for providing a detailed spectrum from soft to hard X--ray energies. This will allow us to disentangle the contribution of soft black body reflection (if any) and hard Comptonized spectral components as well as the detection of discrete emission/absorption features (if present). In particular we will be able to study the energy spectrum of these sources which is usually observed to be quite hard even in outburst in a broad band energy range and with unprecedented high sensitivity above 20 keV. The INTEGRAL observation will also allow a timing analysis in an interesting and yet unexplored energy range.This proposal was submitted for the INTEGRAL A02 and was approved by the TAC with the highest priority but has not been triggered so far. For the A03 program we have proposed for simultaneous observations with XMM-Newton. [truncated! Please see actual data for full text]